IEEE Standard 802.16 defines a set of air interfaces (WirelessMan™ interfaces) for access systems supporting multimedia services, in order to provide access to buildings through exterior antennas communicating with a central base station. Wireless access is a cost-effective alternative to the conventional cabled access. The standard currently defines access specifications for both fixed and nomadic or mobile users, in case of mobility at vehicular speed.
The standard provides a common MAC layer protocol supporting a wide range of physical layer specifications. The IEEE standard MAC protocol has been designed especially for point to multipoint applications, in which each communication channel must accommodate a great number of terminals and each terminal in turn may be shared by multiple users requiring a wide variety of services and using a wide variety of transport protocols.
According to the standard, the data traffic related to a certain service flow is transported, between peer MAC layers in the base station and a terminal or subscriber station, on the so-called transport connections. Each connection is allotted to a single type of service so that several connections exist between a base station and a terminal or subscriber station to allow handling different type of services. Each connection is identified by a connection identifier that is in turn related with a service flow identifier, defining the Quality of Service (QoS) parameters of the service flow associated with that connection.
Within the MAC layer of a transmitting station, the so-called Service-Specific Convergence Sublayer provides for any transformation of external (higher-layer) protocol data units (PDUs) into the MAC service data units (SDUs) that are to be transported over a connection. The selection of the proper connection onto which a data unit will be transported is performed by the Service-Specific Convergence Sublayer through a classification operation, that is a check on whether certain protocol-specific parameters are matched in the data unit to be forwarded. Once classified, a PDU will be encapsulated into a MAC SDU and actually forwarded onto a connection.
Currently, convergence sublayer specifications are defined for both packets and ATM (Asynchronous Transfer Mode) cells, and the present invention is related with packet handling.
In the case of data packets, each classification rule generally defines a set of parameters that are to be matched by the values of specific fields of a packet. Moreover, a classification rule is associated with a priority index, defining the order in which the different classification rules concerning a same service flow are to be applied. When there is a packet to be transmitted, the classification rules are applied to it, starting from the one with higher priority. If all parameters listed in a classification rule match the associated packet fields, the packet is forwarded using the connection associated to the classification rule. If a packet fails to match any classification rule, the convergence sublayer shall discard it.
The standard currently defines a certain number of parameters, but a classification rule needs not to contain all of the parameters defined for the relevant protocol. In this respect, the standard specifies that, if a parameter is omitted in a classification rule, the comparison of the associated field of the packet is irrelevant.
However, in case of subscriber and base stations operating in environments such as a LAN (local Area Network), a problem arises. The standard defines classification rules for traffic packets of data transmission protocols, and mentions, as examples, Internet protocol, Point-to-Point protocol, and Ethernet protocol. In a LAN environment, two entities involved in a communication mutually exchange, besides traffic packets, network control and management packets, which may belong to many different protocols. An example could be the packets relevant to the automatic dialogue between two personal computers that must become connected in order to exchange data. Those network control and management packets are indispensable to permit communication between the two entities, and therefore they too have to be forwarded over a connection established between the two entities at the air interface. The flow of such network control and management packets is completely transparent to the operator that has defined the connections and the classification rules, and such packets generally will not match any data classification rule. Moreover, such packets will not be recognised as MAC management packets to be forwarded on a management connection. Thus, unless some measure is taken, the risk exists that the MAC layer of a LAN entity, when receiving such packets, does not forward them to the peer entity, thereby making communication impossible.
The person of ordinary skill in the art, when confronting with the problem, will consider that the standard requires that some classification rule is matched in order a packet can be forwarded on a connection, and thus he/she will be induced to define further classification rules, as many as are the possible values of a certain packet field. For instance, should the network control and management packet flow be based on an IP protocol, one could imagine that the Type of Service field in the IP packets identifies also those packet kinds and define a new classification rule for each type of service value. This is not a practical approach and, moreover, it does not work for non-IP packets.
By generalising such way of solving the problem, it could be said that the person of ordinary skill in the art, in order to obtain a classification rule that allows mapping also the network control and management packets onto the MAC layer connections, should define a matching parameter for each protocol. Again, apart from the bulk of work involved in such way of operation, it is almost impossible to know a priori all types of network control and management protocols that can be encountered.